LONDON (Reuters) - Cellular phones do not pose short-term health risks, but it remains too soon to say whether they can cause brain cancer or whether children face greater risks than adults, British scientists said on Wednesday.

Publishing the largest UK investigation into possible health problems from mobile technology, scientists said the six-year program found no evidence that short-term mobile phone use affected brain function or could cause brain cancer.

But Professor Lawrie Challis, chairman of the 8.8 million pound ($17.90 million) Mobile Telecommunications and Health Research (MTHR) Program, said studies so far had included few participants who had used cell phones for 10 years or longer.

"We cannot rule out the possibility at this stage that cancer could appear in a few years' time," he told a news conference. "Most cancers take 10 years to appear."

Challis also noted that the UK studies that made up the report had not yet examined children. British scientists had shied away from exposing children to radio-frequency (RF) fields, which are generated by devices such as mobile phones and phone masts, for ethical reasons, he said.

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However, he noted that it was possible for children to be more sensitive to RF radiation than adults and said a second MTHR program was underway, involving 200,000 people in Denmark, Finland, Sweden and Britain.

In the meantime, he stopped short of advising parents against allowing children to use mobile phones as a precautionary measure. "I'm afraid it's up to someone else to give advice," he said.

The MTHR Program was jointly funded by the government and telecoms industry. The telecoms industry, however, merely "signed the checks", Challis said.

Scientists around the world have been monitoring the effects of radio-frequency fields on human health for around 60 years.

Although evidence to date has cleared mobile phone technology of health risks, public concern is rising as more and more adults and children rely increasingly heavily on the technology for everyday communication.